The human eye functions to provide vision by transmitting and refracting light through a clear outer portion called the cornea, and further focusing the image by way of a lens onto the retina at the back of the eye. The quality of the focused image depends on many factors including the size, shape and length of the eye, and the shape and transparency of the cornea and lens.
When trauma, age, disease or other malady cause an individual's natural crystalline lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is often referred to as a cataract. The treatment for this condition is surgical removal of the natural crystalline lens and implantation of an intraocular lens (IOL).
While early IOLs were made from hard plastic, such as polymethylmethacrylate (PMMA), soft, foldable IOLs made from silicone, soft acrylics and hydrogels have become increasingly popular because of the ability to fold or roll these soft lenses and insert them through a smaller incision. Several methods of rolling or folding the lenses are used. One popular method is an injector cartridge that folds the lenses and provides a relatively small diameter lumen through which the lens may be pushed into the eye, usually by a soft tip plunger. One commonly used injector cartridge design is illustrated in U.S. Pat. No. 4,681,102 (Bartell), and includes a split, longitudinally hinged cartridge. Other designs are illustrated in U.S. Patent Nos. 5,494,484 and 5,499,987 (Feingold) and U.S. Pat. Nos. 5,616,148 and 5,620,450 (Eagles, et al.), the entire contents of which are incorporated herein by reference. Still other cartridges are described in U.S. Pat. No. 5,275,604 (Rheinish, et al.), U.S. Pat. No. 5,653,715 (Reich, et al.) and U.S. Pat. No. 5,947,876 (Van Noy, et al.), the entire contents of which are incorporated herein by reference.
At least a portion of the lumen of the cartridge typically becomes progressively smaller (i.e., smaller in cross-sectional area) closer to the nozzle or exit point of the cartridge and the IOL typically becomes rolled, folded and/or compressed as it travels along this portion of the lumen. To foster the movement of the IOL along the lumen, it is generally desirable for the tip of plunger to substantially fill the cross-sectional area of the lumen as the plunger is moved along the length of the lumen. By substantially filling the cross-sectional area, the plunger tip helps ensure that an IOL is reliably pushed along the lumen without a portion of the IOL becoming undesirably trapped between the plunger tip and the cartridge.
To allow the plunger tip to move along the progressively smaller cross-sectional area while continuing to substantially fill the cross-sectional area of the lumen, the plunger tip would traditionally be formed of a soft compressible material that is compressed as it travels along the lumen. This approach can be problematic however. The amount of compression of the plunger tip can become undesirably high particularly toward the nozzle of the cartridge where the cross-sectional area of the lumen can become quite small. In turn, such compression can cause undesirable resistance to travel of the plunger along the lumen as well as other undesirable effects.
Thus, it would be quite desirable to provide an intraocular lens delivery device having a plunger that includes a plunger tip wherein the plunger tip can compress as it moves along a lumen that is becoming progressively smaller and wherein the plunger tip avoids the development of undesirably high forces associated with conventional soft tips.